This invention relates to aromatic amine-containing epoxy resin compositions. In one aspect, the invention relates to the preparation of lightly-crosslinked thermoset materials having enhanced outlife.
It is known that epoxy resin formulations can be prepared which exhibit a balance of high glass transition temperature and toughness which make them good candidates for matrix resins in aerospace composites. Such formulations typically include a difunctional epoxy resin, a difunctional amine and a small quantity, in relation to the difunctional amine, of a multifunctional crosslinking agent. The formulations are designed so that, during the cure process, chain extension of the diepoxide by the diamine is the predominant reaction, with a minor degree of crosslinking occurring through the multifunctional component. The resulting "lightly-crosslinked thermosets" have enhanced toughness compared to fully-crosslinked materials.
In the application of such formulations to prepare composite materials, a "prepreg", or partially-cured reinforced epoxy, is prepared in an intermediate step in the fabrication of a composite part. "Outlife" is the period of time over which the prepreg remains in processable form. Diamines typically used in lightly-crosslinked thermoset formulations tend to have a short outlife, limiting the time over which the prepreg can be handled without refrigeration. It would be desirable to prepare lightly-crosslinked thermoset formulations which have longer outlife.
It is therefore an object of the invention to prepare epoxy resin-based lightly-crosslinked thermoset formulations having longer outlife.